This report describes the NETWORK CONTROL CENTER (NCC) program used in the ARPA Network. The information in the report will explain the functions, structure, and major routines of the NCC program in detail, with diagrams included where helpful. The ARPA Network provides a capability for geographically separated computers, called Hosts, to communicate with each other via common-carrier circuits. Each Host is connected to a small local computer called an Interface Message Processor (IMP); each IMP is connected to several other IMPs via wideband communications lines. The IMPs, most of which are virtually identical, are programmed to store and forward messages to their neighbor IMPs based on address information contained in each message.